There are many web sites out there devoted to removing viruses and malware from your computer. All of them describe long and difficult processes required to identify and remove unwanted software. What makes the removal difficult is that many viruses and malware hide in memory. As you remove infected files from disk, the program in memory adds itself back to another location.
By far the fastest and easiest way to remove viruses and malware is to remove the hard drive and scan it in a different computer. By doing this, you ensure that the virus or malware is not running in memory when the scan is performed. As a best practice you should scan with multiple tools to be sure you catch everything.
I do this by using external USB enclosures for hard drives. I have three separate enclosures for SATA 3.5 inch, PATA 3.5 inch, and PATA 2.5 inch drives. This allows me to externally mount both desktop and laptop drives.
As an alternative, you can boot up by using something like the Ultimate Boot CD for Windows and scan from there. It gets you to the same place, but you are limited to the tools included on that CD instead of your preferred antivirus tools.